The present invention relates to various aspects of internal combustion engine orientation, the disposition of engine ancillaries and their constructive combination, including a xe2x80x9cwet sumpxe2x80x9d engine lubrication system and a turbocharger location, installation and lubrication for an inverted engine, in particular one configured for aircraft propulsion.
The diversity of (multi-)cylinder configurations, for (aircraft) piston engines, typically with a single common crankshaft toward the bottom of the engine, include, for example: (a) a single-file row (i.e. an xe2x80x9cin-linexe2x80x9d configuration); (b) multiple, discrete, xe2x80x9cangularly-splayedxe2x80x9d, or angularly offset, xe2x80x9crowsxe2x80x9d (albeit there may be only one cylinder in each row) xe2x80x94such as a xe2x80x9cVxe2x80x9d or xe2x80x9cWxe2x80x9d configuration; (c) in rows opposed, either horizontally, vertically, or at some other angle (e.g. a xe2x80x9cflatxe2x80x9d configuration); and (d) individually, around a common crankshaft axis, generally equi-angularly spaced, in one or more planes (e.g. a xe2x80x9cradialxe2x80x9d configuration).
There also have been some engines with multiple crankshafts xe2x80x94for example, with cylinders arranged in an xe2x80x9cHxe2x80x9d configuration (in effect, two xe2x80x98flatxe2x80x99 engines, sharing a single common crankcase), or with two pistons per cylinder working in opposition in various xe2x80x9copposed-pistonxe2x80x9d arrangements.
It is known to invert an in-line, or xe2x80x9cVxe2x80x9d engine configuration so that the cylinders are below the crankshaft, which is thus toward the top of the engine. A prime advantage of such engine inversion, for aircraft propeller propulsion is that the crankshaft sits higher on the engine, and so a propeller mounted directly upon it will be farther from the ground. At critical flight phases of take-off and landing, it is important to maintain adequate clearance between the propeller and the ground. The object is to reduce the chance of accidental damage, allowing for undercarriage travel and fuselage forward tipping moment about the undercarriage.
Other ways to improve ground clearance include lengthening the undercarriage in order to raise the whole aircraft further from the ground, reducing the diameter of the propeller, and raising the engine installation in the aircraft. All of these have drawbacks, however. It is thus well-established for smaller aircraft that use directly-driven propellers (i.e. propellers mounted directly upon a crankshaft end), to use an inverted engine arrangement.
Engines that are not inverted, that is which have the crankshaft generally at the bottom of the crankcase and the cylinders generally upright or vertical with the cylinder heads uppermost (in the case of in-line engines), commonly have a wet sump lubrication system and rely upon a gravity return of a recirculatory lubricant (oil). More specifically, a lower part of the crankcase is typically extended to provide a reservoir (i.e. the sump) of lubricant (oil). Thus, in practice, a sump body or casing is commonly secured directly to part of the engine body, housing, or casing.
Alternatively, engines may have a dry sump lubrication system and rely upon a pumped recirculatory flow return of lubricant (oil) to a discrete reservoir. Thus, in practice, lubricant (oil) is typically drained away, partly (passively) under gravity, to one or more internal engine collection point(s). Collected (oil) then (actively) pumped (scavenged), or returned by some other positive displacement or pressuredifferential means, to a separate (oil) tank that serves as an (external) engine lubricant (oil) reservoir (i.e. outside an internal engine lubricant path). One dry sump arrangement (e.g. ROTAX(trademark)) uses ambient crankcase pressure to return used oil to an oil tank. Alternatively, the oil may drain naturally from the dry sump to a (separate) oil tank at a lower level. Also, radial engines are known in which xe2x80x9cusedxe2x80x9d oil from each cylinder head, as well as the crankcase, is returned to a separate oil tank.
Hitherto, inverted aircraft engines have used a dry sump arrangement, that is with xe2x80x9cusedxe2x80x9d oil being returned to a (discrete, dedicated) tank, disposed externally of the engine, by draining (passively) under gravity, and/or being (actively) drawn away by an oil (scavenge) pump.
According to one aspect of the present invention, an inverted engine has a wet sump lubrication system with a combined sump casing and cylinder head, camshaft or valve gear, cover. Elimination of a separate oil tank and its associated feed supply and recirculatory return pipe-work or plumbing, provides the advantages of an integral oil system, such as an on-board or integral sump. The wet sump system removes the inherent disadvantages of the dry sump arrangement. Thus, it is simpler with fewer parts, pipes, joints, etc., that may fail or leak, and the integration of oil system and engine also creates a single stand-alone package.
Installation issues are significant for the light aircraft market which is sensitive to first cost and ongoing running and maintenance costs and may also use installers with limited skills such as builders of kit aircraft. By combining an inverted engine configuration with the cam shaft in the head and wet sump lubrication according to the present invention, lubricant (oil) in the sump can provide constant lubrication by indirect splash and/or direct immersion to the camshaft lobes. This is particularly important at engine start-up. During normal operation, there will be oil mist/splash lubrication present and so force-feed lubrication of the camshaft and valve train may not be necessary thus simplifying the design.
Another potential problem of non-inverted engines where a camshaft is generally mounted high in the engine, is that the cam lobes and followers can become dry during periods of engine non-use. Critical wear surfaces can thus be scored, scuffed and otherwise damaged due to lack of lubricant at engine start-up. In a wet sump inverted engine according to the present invention, the cam can remain flooded with oil even during long periods of non-use, thus eliminating or minimizing the possibility of dry cam lobes.
Aside from cam-in-head configurations, a similar constant lubrication benefit could be provided for rocker arms and other valve gear components commonly used with push-rod type valve actuation. Advantageously, with a cam-in-head configuration, a rotary oil pump and fittings could be mounted close to the oil sump and integrated with, or coupled to a camshaft drive. Indeed, the pump could be mounted upon the camshaft itself.
A wet sump lubrication system in an inverted engine, according to the invention, can be applied to in-line or V configurations. An engine may be of otherwise conventional design. This aspect of the invention, along with the various other aspects described elsewhere, taken both individually and collectively, are generally compatible with the following: two, or four-stroke combustion cycles; high, or low-mounted camshafts; multiple cylinders; compression- ignition (xe2x80x98dieselxe2x80x99) combustion; sparkignition combustion; liquid fuel (e.g. gasoline, kerosene, fuel oil or liquefied petroleum gas); and gaseous fuel.
The engine may also be equipped with a turbo-super-charger or multiple turbo-super-chargers which may be connected in series or parallel. A downstream turbine may be fitted, and geared to provide extra power to the crankshaft (usually known as xe2x80x9cturbo-compoundingxe2x80x9d). A mechanically-driven super-charger, or multiple super-chargers, may be used in the pressure charging system.